1. Field of the Invention
The present invention relates to lead-free solder that contains no lead (Pb).
2. Description of the Related Art
Electronic component built-in modules each include a substrate and a plurality of electronic components, such as passive components and active components, which are mounted on the substrate by using solder so as to have integrated functions. To mount such electronic components on a substrate of an electronic device, a terminal electrode of the electronic component built-in module and a terminal electrode of the substrate are joined together by solder. Conventionally, Sn—Pb solder has been used to join electronic components together; however, lead-free manufacturing has been promoted with environmental issues as a backdrop, so that lead-free solder is popularly used except in fields related to automobiles and in special situations.
To mount an electronic component built-in module on a substrate by using solder, it is necessary to perform a reflow process to melt the solder. During such a reflow process, in some situations, pieces of solder joining the electronic components included in the electronic component built-in module to the substrate may melt and splash or the positions thereof may shift. To avoid such situations, it is necessary to join the electronic components included in the electronic component built-in module to the substrate by using such solder that does not melt at the reflow temperature that is used for mounting the electronic component built-in module to the substrate. For example, Japanese Laid-open Patent Publication No. 2001-62561 discloses a technique for brazing two members together by using a brazing material that is alloyed so as to have an arbitrary composition in such a manner that, when the two members to be brazed together are heated while being in contact with each other after metal layers that are made of mutually different types of metal and that are alloyed to serve as the brazing material are formed in the manner of stacked layers onto at least one of the two members, at least one of the metal layers is in a liquid phase whereas the other metal layer is caused to melt into the liquid-phase metal layer while a solid-phase state of the other metal layer is being included.